ACTG 356 is a three part, phase I/II open-label study evaluating three different antiretroviral combination regimens (each containing 3 or 4 antiretrovirals) in vertically HIV-infected infants and children 15 days to 3 years of age. The drug combinations under evaluation are: 1)zidovudine/lamivudine/nevirapine; 2) zidovudine/stavudine/nevirapine/ abacavir; and 3) stavudine/lamivudine/nevirapine/nelfinavir. Evaluations include HIV-1 and CD4/CD8 T cell kinetics, activation and maturation. This study also tests the concept that early treatment (i.e. beginning therapy at < 3months of age) with potent, combination antiretroviral therapy will allow the long term control of viral replication with preservation of normal immune function. This study has completed accrual. Treatment and follow- up of patients should be completed by November 2000. Toxicity from these regimens has been tolerable; no preliminary efficacy data are available.